1. Field of the Invention
The invention relates to a transparent heat shielding material, and more particularly to a transparent heat shielding material formed from tungsten oxide with an anion and a cation co-doping.
2. Description of the Related Art
Generally, conventional heat shielding films are mainly made of multi-layered silver film. The fact that silver film is unstable in air is the major disadvantage of conventional heat shielding films. Additionally, conventional heat shielding films need to be formed from multi-layered film and by an expensive sputtering process, such that the fabrication cost of conventional heat shielding films is high.
Other conventional heat shielding films are made of electrically conductive material consisting of transparent oxides, such as antimony tin oxide (ATO) of SnO2:Sb or indium tin oxide (ITO) of SnO2: which has a plasma wavelength of about 1000 nm to 2500 nm. Because the conductivity of the conventional heat shielding film made of transparent conductive oxides is too low, the plasma wavelength thereof is greater than 1000 nm. Accordingly, a partial infrared light with a wavelength between 800 nm and 1000 nm passes through the conventional heat shielding film made of transparent conductive oxides, and the heat shielding function of the conventional heat shielding film is insufficient.
Moreover, another conventional heat shielding film can be made of lanthanum hexaboride (LaB6) material with a plasma wavelength of 700 nm to 1100 nm. The conductivity of the conventional heat shielding film made of LaB6 is high enough to shield against greater levels of infrared light. However, the conventional heat shielding film made of LaB6 absorbs light in a visible light wavelength range such that the color of the conventional heat shielding film made of LaB6 is too deep to satisfy the requirements of high transparency and high heat shielding capability of heat shielding films.
In addition, conventional transparent heat shielding films can be made of tungsten oxide with alkali metal element doping to shield against infrared light. However, while the visible light transmission of the conventional transparent heat shielding films made of tungsten oxide with alkali metal element doping is greater than 70%, the infrared light shielding ability thereof is poor. While the infrared light shielding ability of the conventional transparent heat shielding films made of tungsten oxide with alkali metal element doping is greater than 90%, the visible light transmission thereof is reduced below 70%. Accordingly, the conventional transparent heat shielding films made of tungsten oxide with alkali metal element doping can not achieve high visible light transmission and high infrared light shielding ability at the same time.
Therefore, a transparent heat shielding material, which can be used to form a transparent heat shielding film using a simple and low temperature coating process with a low fabrication cost, and satisfy the requirements of high visible light transmission, high heat shielding ability and high stability is desired.